The roof support structure of a commercial or industrial type building is typically constructed of parallel spaced apart joists or purlins on which are supported the various component elements comprising the roof. The fabrication and constructions of such roofs can vary widely and are exemplified by the disclosures of U.S. Pat. Nos. 2,861,525; 3,694,306; 3,969,863; 4,233,791; 4,303,713; 4,393,634; 4,472,920 and 4,566,239.
Several decades ago, the only essential purpose of a roof on most buildings was to protect and enclose the interior spacing against the weather elements. With the advent of temperature controlled space, particularly air conditioning as now known, the use of insulation associated with the roof structure has become increasingly important. Not only does the insulation provide a greater comfort factor within the conditioned space, but it also serves to reduce the capital cost and operating cost of the conditioning equipment. Common therefore to the current prior art roof constructions is the requirement for a vapor barrier, a predetermined quantity of insulation and a generally protective layer of hard roofing typically in a form of a metal or other suitable overlayer secured to the roof supports. Various types of insulation material are known for that purpose and typically comprise fiberglass, celluloses, rockwool and other materials available for the purpose. Fiberglass blankets, as commonly utilized, contains a vinyl, foil or papered vapor barrier laminated along one face. Characteristically, the lamination of the vapor barrier to the fiberglass tends to crush the fiberglass rendering it less effective as an insulation while creating pin holes in the vapor barrier material. Via such pin holes vapor can penetrate to wet the insulation or condense on the underside of the superposed metal decking. As is well known, wetted insulation has significantly reduced resistance to thermal conductivity than does the same insulation when dry.
Insofar as various roof systems have been disclosed in the patents identified supra, they differ from each other in specific features of construction, method of application, useful longevity, finished appearance, ultimate degree of effectiveness for the intended purpose and/or cost of fabrication. It is known from the above, for example, to support vapor barrier sheeting on the underside of the purlins or to drape the vapor barrier from the top side of the purlins in order to position the insulation in the intervening space between purlins. It will be appreciated that much of the labor expended in the fabrication of such installations is conducted from a ladder, scaffold, or hydraulic lift from below the supports creating a high degree of discomfort to the workmen. Consequently they can be difficult, time consuming and relatively costly to install, not to mention the likelihood of imperfection in workmanship contributed by the personal discomforts associated with the work environment having to work overhead. A further problem associated with the foregoing has been a tendency in such installations to incur vapor leakage through the seams formed between adjacent sections of the vapor barrier causing both rusting of the purlins and metal decking and/or wetting of the insulation, that as mentioned above, deleteriously affects the insulation properties thereof.
Still another form of insulating roof fabrication disclosed in the patents above utilizes a lattice framework underlying the purlins in a positions intervening between the purlins and the rafters. Thereafter the roof is fabricated from above in a machine application of a vapor barrier faced insulation to between the purlins followed by a hard roofing extending over the insulation to represent the exterior exposed decking surface thereof.
The difficulties and complexities of such installations should be readily apparent yet despite recognition of the foregoing problems, a ready solution therefor has not heretofore been known.